Mainstream academic accidentally stumbles across the justification for folkish imperialism:
https://finance.yahoo.com/news/whack-mole-experts-call-hong-041901476.html"Only Hong Kong and China are saying they are trying to eradicate the virus," he said. "It would have worked if other countries did the same but the fact they don’t think that way means the virus is always flowing."
In other words, China would be theoretically justified in invading all non-eradicationist countries, on the condition that it imposes the same eradicationist rules everywhere. It is the non-eradicationist countries preventing the eradication from succeeding, therefore it is justified for the eradicationist countries to invade them. (Similarly, a hypothetical vegan country would be justified in invading all non-vegan countries for the sake of eradicating cruelty to animals, and so on.)
In contrast, wishing to bring progress to additional territories is an invalid reason for invasion. A non-industrial country does not prevent an industrial country from successful industry, therefore the industrial country is unjustified in invading the non-industrial country. A non-compulsory-schooling country does not prevent a compulsory-schooling scountry from successful compulsory schooling, therefore the compulsory-schooling country is unjustified in invading the non-compulsory-schooling country. And so on. (In fact it is the other way round: the non-industrial/non-compulsory-schooling/etc. countries should invade the industrial/compulsory-schooling/etc. countries in order to eradicate industry/compulsory schooling/etc.!)
In general, let X be an idea. If X is something that can succeed only if everyone practices it, invasion to impose X is justified. Whereas if X is something that can succeed with merely a fraction of people practicing it, invasion to spread X is unjustified (but invasion of practitioners by non-practitioners to eradicate X is justified!).
Most fundamentally, consider reproduction. Reproducers are not justified in invading non-reproducers, because reproduction will succeed so long as some people reproduce (irrespective of the remainder not reproducing). On the other hand, non-reproducers are justified in invading reproducers, because non-reproduction will only succeed if everyone refrains from reproducing simultaneously.
So, what is the common feature of all ideas that can succeed only if everyone practices them simultaneously, and what is the common feature of all ideas that can succeed with merely a fraction of people practicing them?